Infection by hepatitis C virus (HCV) is a compelling human medical problem. HCV is recognized as the causative agent for most cases of non-A, non-B hepatitis, with an estimated human sero-prevalence of 3% globally [A. Alberti et al., “Natural History of Hepatitis C,” J. Hepatology, 31, (Suppl. 1), pp. 17-24 (1999)]. Nearly four million individuals may be infected in the United States alone [M. J. Alter et al., “The Epidemiology of Viral Hepatitis in the United States, Gastroenterol. Clin. North Am., 23, pp. 437-455 (1994); M. J. Alter “Hepatitis C Virus Infection in the United States,” J. Hepatology, 31, (Suppl. 1), pp. 88-91 (1999)].
The HCV genome encodes a polyprotein of 3010-3033 amino acids, which has the structure NH2-C-E1-E2-p7-NS2-NS3-NS4A-NS4B-NS5A-NS5B-COOH [Q. L. Choo, et. al., “Genetic Organization and Diversity of the Hepatitis C Virus,” Proc. Natl. Acad. Sci. USA, 88, pp. 2451-2455 (1991); N. Kato et al., “Molecular Cloning of the Human Hepatitis C Virus Genome From Japanese Patients with Non-A, Non-B Hepatitis,” Proc. Natl. Acad. Sci. USA, 87, pp. 9524-9528 (1990); A. Takamizawa et. al., “Structure and Organization of the Hepatitis C Virus Genome Isolated From Human Carriers,” J. Virol., 65, pp. 1105-1113 (1991)]. The HCV nonstructural (NS) proteins are presumed to provide the essential catalytic machinery for viral replication. The NS proteins are derived by proteolytic cleavage of the polyprotein [R. Bartenschlager et. al., “Nonstructural Protein 3 of the Hepatitis C Virus Encodes a Serine-Type Proteinase Required for Cleavage at the NS3/4 and NS4/5 Junctions,” J. Virol., 67, pp. 3835-3844 (1993); A. Grakoui et. al., “Characterization of the Hepatitis C Virus-Encoded Serine Proteinase: Determination of Proteinase-Dependent Polyprotein Cleavage Sites,” J. Virol., 67, pp. 2832-2843 (1993); A. Grakoui et. al., “Expression and Identification of Hepatitis C Virus Polyprotein Cleavage Products,” J. Virol., 67, pp. 1385-1395 (1993); L. Tomei et. al., “NS3 is a serine protease required for processing of hepatitis C virus polyprotein”, J. Virol., 67, pp. 4017-4026 (1993)].
The HCV NS protein 3 (NS3) contains a serine protease activity that helps process the majority of the viral enzymes, and is thus considered essential for viral replication and infectivity. The first 181 amino acids of NS3 (residues 1027-1207 of the viral polyprotein) have been shown to contain the serine protease domain of NS3 that processes all four downstream sites of the HCV polyprotein [C. Lin et al., “Hepatitis C Virus NS3 Serine Proteinase: Trans-Cleavage Requirements and Processing Kinetics”, J. Virol., 68, pp. 8147-8157 (1994)]. The NS3 protein also possesses helicase and NTPase domains.
The HCV NS3 serine protease and its associated cofactor, NS4A, help process all of the viral enzymes, and are thus considered essential for viral replication. This processing appears to be analogous to that carried out by the human immunodeficiency virus aspartyl protease, which is also involved in viral enzyme processing. HIV protease inhibitors inhibit viral protein processing and are potent antiviral agents in humans, indicating that interrupting this stage of the viral life cycle results in therapeutically active agents. Consequently the analogous HCV NS3 protease and NS4A are attractive targets for drug discovery.
Several potential HCV protease inhibitors have been described [PCT Publication Nos. WO 02/18369, WO 02/08244, WO 00/09558, WO 00/09543, WO 99/64442, WO 99/07733, WO 99/07734, WO 99/50230, WO 98/46630, WO 98/17679 and WO 97/43310; U.S. Pat. No. 5,990,276; M. Llinas-Brunet et al., Bioorg. Med. Chem. Lett., 8, pp. 1713-18 (1998); W. Han et al., Bioorg. Med. Chem. Lett., 10, 711-13 (2000); R. Dunsdon et al., Bioorg. Med. Chem. Lett., 10, pp. 1571-79 (2000); M. Llinas-Brunet et al., Bioorg. Med. Chem. Lett., 10, pp. 2267-70 (2000); and S. LaPlante et al., Bioorg. Med. Chem. Lett., 10, pp. 2271-74 (2000)]. Nevertheless, the current understanding of HCV has not led to any other satisfactory anti-HCV agents or treatments. The only established therapy for HCV disease is interferon treatment. However, interferons have significant side effects [M. A. Wlaker et al., “Hepatitis C Virus: An Overview of Current Approaches and Progress,” DDT, 4, pp. 518-29 (1999); D. Moradpour et al., “Current and Evolving Therapies for Hepatitis C,” Eur. J. Gastroenterol. Hepatol., 11, pp. 1199-1202 (1999); H. L. A. Janssen et al. “Suicide Associated with Alfa-Interferon Therapy for Chronic Viral Hepatitis,” J. Hepatol., 21, pp. 241-243 (1994); P. F. Renault et al., “Side Effects of Alpha Interferon,” Seminars in Liver Disease, 9, pp. 273-277. (1989)] and induce long term remission in only about 25% of cases [O. Weiland, “Interferon Therapy in Chronic Hepatitis C Virus Infection”, FEMS Microbiol. Rev., 14, pp. 279-288 (1994)]. Moreover, the prospects for effective anti-HCV vaccines remain uncertain.
Thus, there is a need for more effective anti-HCV therapies. Such inhibitors would have therapeutic potential as protease inhibitors, particularly as serine protease inhibitors, and more particularly as HCV NS3 protease inhibitors. Specifically, such compounds may be useful as antiviral agents, particularly as anti-HCV agents. Consequently, an assay that can identify more effective HCV NS3 protease inhibitors is needed.